Control apparatus for continuously-variable transmission of vehicle

ABSTRACT

A control apparatus for an automatic transmission includes a control section having a target secondary pressure setting section configured to set a target secondary pressure within a strength limit of the belt, and an operation switching section configured to switch a shift operation from a normal speed to a high speed higher than the normal speed when a predetermined condition is satisfied. The control section is configured to control the secondary pressure regulating valve by a feedback control based on the target secondary pressure and the actual secondary pressure sensed by the hydraulic pressure sensor. The target secondary pressure setting section is configured to modify the target secondary pressure by adding a predetermined quantity when a correction initiation condition is satisfied, the condition initiation including a first condition that the shift operation is performed at a high speed by switching of the operation switching section.

BACKGROUND OF THE INVENTION

The present invention relates to a control apparatus for an automatictransmission of a vehicle which is configured to control a transmissiongear ratio by using a hydraulic pressure of a hydraulic fluid.

A belt-type continuously-variable transmission includes a primary pulley(driving pulley), a secondary pulley (driven pulley), and a belt woundaround the primary pulley and the secondary pulley. The primary pulleyincludes a fixed pulley (sheave) integrally formed with a shaft (primaryshaft) serving as a rotation axis, and a movable pulley (slidablesheave) arranged to be moved in an axial direction of the primary shaft,and located at a position to confront the fixed pulley of the primarypulley. The secondary pulley includes a fixed pulley (sheave) integrallyformed with a shaft (secondary shaft) serving as a rotation axis, and amovable pulley (sheave) arranged to be moved in an axial direction ofthe secondary shaft, and located at a position to confront the fixedpulley of the secondary pulley. The belt is contacted, under pressure,with a V-shaped groove defined by the fixed pulley and the movablepulley of the primary pulley, and with a V-shaped groove defined by thefixed pulley and the movable pulley of the secondary pulley, andaccordingly power transmission is performed by the compressive contactbetween the belt and each of the primary and the secondary pulley.

The movable pulley of the primary pulley is arranged to move axiallytoward or move axially apart from the fixed pulley of the primary pulleyby regulating a hydraulic pressure within a hydraulic chamber formed ona back surface (or rear surface) of the movable pulley of the primarypulley. The movable pulley of the secondary pulley is arranged to moveaxially toward or move axially apart from the fixed pulley of thesecondary pulley by regulating a hydraulic pressure within a hydraulicchamber formed on a back surface (or rear surface) of the movable pulleyof the secondary pulley. This movements (stroke displacement) of themovable pulleys varies groove widths of the V-shaped groovesrespectively, and adjust effective radiuses of rotation of the primaryand secondary pulleys. Consequently, it is possible to vary a powertransmission ratio from the primary pulley to the secondary pulley in astepless manner.

In a case in which a transmission gear ratio (pulley ratio) is increased(that is, in a case in which the transmission gear ratio is shifted to alow side), the hydraulic pressure (an actual secondary pressure) of thehydraulic chamber of the secondary pulley is increased to move themovable pulley of the secondary pulley toward the fixed pulley of thesecondary pulley. Consequently, the groove width of the V-shaped grooveof the secondary pulley is decreased, and the effective radius of therotation of the secondary pulley is increased. In this state, the radiusof the rotation of the primary pulley is decreased as the radius of therotation of the secondary pulley is increased because length of the beltdoes not vary, so that it is possible to increase the pulley ratio.

In the conventional belt-type continuously-variable transmission, at theshift operation, a final target pulley ratio is firstly set inaccordance with a vehicle speed and a throttle opening (TVO). Then, atarget time constant (a constant which correlates to the shift speed,and which is set appropriately (arbitrarily)), and which is set at eachof various shifts such as an upshift, a downshift, and adepression-induced downshift (downshift accompanying the driver'sdepression) is set. The actual secondary pressure is controlled inaccordance with the shift speed, and the shift operation is performed ata predetermined shift speed. This actual secondary pressure iscontrolled by the feedback based on a target secondary pressure and theactual secondary pressure sensed by a hydraulic pressure sensor.

SUMMARY OF THE INVENTION

Incidentally, in a case such as the depression-induced downshift atwhich rapid acceleration is required, it is desired that an accelerationresponse is further improved. For improving this acceleration response,it is requested to improve a shift response from the accelerator pedaldepression until the actual pulley ratio is varied to the target pulleyratio on the low side. To improve the shift response, the shift speed(corresponding to a pulley stroke speed in the belt-typecontinuously-variable transmission) at the change of the pulley ratiomay be set greater than the shift speed of the conventionaltransmission, so that the actual pulley ratio is rapidly shifted to thetarget pulley ratio.

In particular, the transmission torque is increased in order to performthe shift down for the acceleration at the high speed, and belt slippagetends to occur. Accordingly, it is necessary to increase the targetsecondary pressure for preventing the belt slippage. However, in a casein which the shift speed is increased when the secondary pressure iscontrolled by the feedback control, problems are caused as describedlater. That is, in the belt-type continuously-variable transmission, ina case of performing an operation to rapidly decrease the actualsecondary pressure when the transmission gear ratio is shifted to thehigh side, the actual secondary pressure is extremely decreased than thetarget secondary pressure for the rapid decrease in the actual secondarypressure, and the belt slippage may occur. Accordingly, an orifice isprovided in the oil passage between the movable pulley (hydraulicchamber of the movable pulley) of the secondary pulley and a secondarypressure regulating valve arranged to supply the secondary pressure, andit is possible to suppress the rapid decrease in the actual secondarypressure by the orifice.

On the other hand, the hydraulic pressure sensor which is configured tosense the actual secondary pressure used by the feedback control of thesecondary pressure is provided between the secondary pressure regulatingvalve configured to supply the desired pressure to the secondary pulley,and the orifice provided in the oil passage between the secondarypressure regulating valve and the secondary pulley. In this way, thehydraulic pressure sensor is provided between the secondary pressureregulating valve and the orifice. When the pressure between the orificeand the secondary pressure regulating valve is increased, the hydraulicpressure is increased at a position of the hydraulic pressure sensor,and the hydraulic pressure sensor senses this increase of the hydraulicpressure. However, in this case, the hydraulic pressure of the movablepulley (the hydraulic chamber of the movable pulley) of the secondarypulley is not immediately increased for the effect of the orifice, andthe hydraulic sensor outputs a value larger than the actual secondarypressure.

Accordingly, the sensed pressure of the hydraulic pressure sensor may besufficiently increased, though the actual secondary pressure is low. Thefeedback control of the secondary pressure is performed based on thesensed pressure of the hydraulic pressure sensor. Therefore, it ispossible to increase the actual secondary pressure sufficiently evenwhen the feedback control of the secondary pressure is performed.Consequently, the belt slippage may be incurred for the insufficiency ofthe actual secondary pressure.

In particular, the flow velocity and the flow pressure of the hydraulicfluid within the oil passage is increased as the shift speed isincreased, and error between the sensed actual secondary pressure andthe actual pressure within the hydraulic chamber of the secondary pulleyis increased. Accordingly, it is not possible to exclude the influenceof the difference between the actual secondary pressure and the sensedpressure of the hydraulic pressure sensor when the shift speed isincreased to an extent. The belt slippage may be incurred for thedeficiency of the actual secondary pressure as described above, andtherefore some treatment is needed.

It is, therefore, an object of the present invention to provide acontrol apparatus for a belt-type continuously-variable transmissionwhich is devised to prevent a belt slippage by increasing an actualsecondary pressure in a case of increasing a shift speed at a shift.

According to one aspect of the present invention, a control apparatusfor an automatic transmission of a vehicle, the control apparatuscomprises: a primary pulley including a movable pulley, the primarypulley being connected with an input; a secondary pulley including amovable pulley, the secondary pulley being connected with an output; abelt wound around the primary pulley and the secondary pulley; a shiftcontrol valve configured to regulate a hydraulic pressure acting on themovable pulley of the primary pulley, and to control a target pulleyratio between the primary pulley and the secondary pulley; a secondarypressure regulating valve configured to regulate a secondary hydraulicpressure acting on the movable pulley of the secondary pulley, and toregulate an engagement pressure between the belt and each of the primarypulley and the secondary pulley; an orifice disposed in an oil passagebetween the movable pulley of the secondary pulley and the secondarypressure regulating valve; a hydraulic pressure sensor disposed betweenthe secondary pressure regulating valve and the orifice in the oilpassage, and configured to sense an actual secondary pressure; and acontrol section including a target secondary pressure setting sectionconfigured to set the target secondary pressure within a strength limitof the belt so as to prevent a slippage between the belt and each of theprimary pulley and the secondary pulley, and an operation switchingsection configured to switch a shift operation from a normal speed to ahigh speed higher than the normal speed when a predetermined conditionis satisfied, the control section being configured to control thesecondary pressure regulating valve by a feedback control based on thetarget secondary pressure and the actual secondary pressure sensed bythe hydraulic pressure sensor, the target secondary pressure settingsection being configured to modify the target secondary pressure byadding a predetermined quantity when a correction initiation conditionis satisfied, the correction initiation condition including a firstcondition that the shift operation is performed at a high speed byswitching of the operation switching section.

According to another aspect of the invention, a control method for anautomatic transmission of a vehicle including a primary pulley includinga movable pulley, the primary pulley being connected with an input, asecondary pulley including a movable pulley, the secondary pulley beingconnected with an output, a belt wound around the primary pulley and thesecondary pulley, a shift control valve configured to regulate ahydraulic pressure acting on the movable pulley of the primary pulley,and to control a target pulley ratio between the primary pulley and thesecondary pulley, a secondary pressure regulating valve configured toregulate a secondary hydraulic pressure acting on the movable pulley ofthe secondary pulley, and to regulate an engagement pressure between thebelt and each of the primary pulley and the secondary pulley, an orificedisposed in an oil passage between the movable pulley of the secondarypulley and the secondary pressure regulating valve, and a hydraulicpressure sensor disposed between the secondary pressure regulating valveand the orifice in the oil passage, and configured to sense an actualsecondary pressure, the control method comprises: setting the targetsecondary pressure within a strength limit of the belt so as to preventa slippage between the belt and each of the primary pulley and thesecondary pulley; switching a shift operation from a normal speed to ahigh speed higher than the normal speed when a predetermined conditionis satisfied; controlling the secondary pressure regulating valve by afeedback control based on the target secondary pressure and the actualsecondary pressure sensed by the hydraulic pressure sensor; andmodifying the target secondary pressure by adding a predeterminedquantity when a correction initiation condition is satisfied, thecorrection initiation condition including a first condition that theshift operation is performed at a high speed by switching of theoperation switching section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a control block diagram showing a shift control section of acontrol apparatus which is configured to calculate a target secondarypressure for a belt-type continuously-variable transmission according toan embodiment of the present invention.

FIG. 2 is a block diagram showing the continuously-variable transmissionaccording to the embodiment of the present invention, and a shiftcontrol system of the continuously-variable transmission.

FIG. 3 is a block diagram showing the shift control system of thecontinuously-variable transmission of FIG. 2.

FIG. 4 is a diagrammatic view showing a hydraulic pressure circuitaround a secondary pulley of the continuously-variable transmission ofFIG. 2.

FIG. 5 is a functional block diagram showing a shift control section ofthe continuously-variable transmission of FIG. 2.

FIG. 6 is a flow chart showing a control process of thecontinuously-variable transmission of FIG. 2.

FIG. 7 is a graph showing a time dependent variation between an actualpulley ratio and a transmission gear ratio command value at a shift, inthe continuously-variable transmission of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1˜7 show views illustrative of a hydraulic pressure controlapparatus for a belt-type continuously-variable transmission of avehicle which is employed as a continuously-variable transmission in anembodiment of the present invention. FIG. 1 is a functional blockdiagram showing a shift control section of a transmission controllerconfigured to control a step motor. FIG. 2 is a diagrammatic viewshowing the continuously-variable transmission and a shift controlsystem of the continuously-variable transmission. FIG. 3 is a blockdiagram showing a configuration of a hydraulic pressure control systemof the continuously-variable transmission of FIG. 2. FIG. 4 is a circuitdiagram showing a hydraulic circuit around a secondary pulley of thetransmission of FIG. 2. FIG. 5 is a view showing a section calculating atarget secondary pressure. FIG. 6 is a flow chart showing a controlprocess performing by a control system (a high speed shift judgmentsection). FIG. 7 is a graph showing a time-dependent variation between astep motor command value and an actual pulley ratio.

As shown in FIG. 2, belt-type continuously variable transmission 1includes a primary pulley 2 and a secondary pulley 3 each provided witha V-shaped groove, and disposed so that the V-shaped grooves of primarypulley 2 and secondary pulley 3 are aligned with each other, and aV-belt 4 wound around the V-grooves of primary pulley 2 and secondarypulley 3. An engine 5 is disposed in an axis of primary pulley 2. Atorque converter 6 and a forward-reverse switching mechanism 7 aredisposed between engine 5 and primary pulley 2. Torque converter 6 isdisposed between engine 5 and forward-reverse switching mechanism 7.Torque converter 6 is provided with a lockup clutch.

Forward-reverse switching mechanism 7 includes a double pinion planetarygear mechanism having a sun gear connected through torque converter 6with engine 5, and a career (a planetary career) connected with primarypulley 2. Forward-reverse switching mechanism 7 further includes aforward clutch arranged to directly connect the sun gear and the careerof the double pinion planetary gear mechanism, and a reverse brakearranged to fix a ring gear. Forward-reverse switching mechanism 7 isarranged to receive input rotation from engine 5 through torqueconverter 6, and to directly output this input rotation to primarypulley 2 at the engagement of the forward clutch. Forward-reverseswitching mechanism 7 is arranged to receive the input rotation fromengine 5 through torque converter 6, to reverse and decelerate the inputrotation, and to output this rotation to primary pulley 2 at theengagement of the reverse brake.

Consequently, the rotation to primary pulley 2 is transmitted throughV-belt 4 to secondary pulley 3, and then transmitted to wheels (notshown). Primary pulley 2 includes a fixed pulley (fixed sheave) 2 a, anda movable pulley (movable sheave) 2 b movable in the axial direction,and defining the V-shaped groove of primary pulley 2 with fixed pulley 2a. Secondary pulley 3 includes a fixed pulley (fixed sheave) 3 a, and amovable pulley (movable sheave) 3 b movable in the axial direction, anddefining the V-shaped groove of secondary pulley 3 with fixed pulley 3a. Primary pulley 2 is arranged to vary a groove width of the V-shapedgroove of primary pulley 2 by the movement of movable pulley 2 b, and tovary a contact radius of V-belt 4 on primary pulley 2. Secondary pulley3 is arranged to vary a groove width of the V-shaped groove of secondarypulley 3 by the movement of movable pulley 3 b, and to vary a contactradius of V-belt 4 on secondary pulley 3. The continuously-variabletransmission is arranged to vary a transmission gear ratio (pulley ratioor gear ratio) continuously during power transmission, by varying thecontact radiuses of V-belt 4 on primary and secondary pulleys 2 and 3.

A primary chamber 2 c of movable pulley 2 b of primary pulley 2 issupplied with a primary pressure (or primary thrust) Ppri made from aline pressure serving as a source pressure, so that movable pulley 2 bis moved toward fixed pulley 2 a. Consequently, primary pulley 2 isfrictionally engaged with V-belt 4. A secondary chamber 3 c of movablepulley 3 b of secondary pulley 3 is supplied with a secondary pressure(or secondary thrust) Psec made from the line pressure serving as thesource pressure, so that movable pulley 3 b is moved toward fixed pulley3 a. Consequently, secondary pulley 3 is frictionally engaged withV-belt 4. Therefore, the power transmission between primary pulley 2 andsecondary pulley 3 is performed by using frictional engagement betweenthe V-belt and each of primary and secondary pulleys 2 and 3.

At a shift, each of V-groove widths of primary and secondary pulleys 2and 3 is varied by a difference of the thrust between primary pressurePpri and secondary pressure Psec which are generated in accordance witha target pulley ratio. Accordingly, it is possible to vary the contactradiuses of V-belt 4 on primary and secondary pulleys 2 and 3, and toshift to a desired pulley ratio. To regulate primary pressure Ppri andsecondary pressure Psec in this way, there are provided a shift controlhydraulic circuit 11 and a transmission controller 12. Shift controlhydraulic circuit 11 performs control operations as described later, inresponse to a signal from transmission controller 12.

Transmission controller 12 receives a signal from a primary pulleyrotation sensor 13 arranged to sense a primary pulley rotational speedNpri, a signal from a secondary pulley rotation sensor 14 arranged tosense a secondary pulley rotational speed Nsec, a signal from ahydraulic pressure sensor (a secondary pressure sensor) 15 arranged tosense secondary pressure Psec, and a signal from a hydraulic pressuresensor (a primary pressure sensor) 16 arranged to sense primary pressurePpri.

(hydraulic system) FIG. 3 shows a configuration of shift controlhydraulic circuit 11 and transmission controller 12 as described above.

Shift control hydraulic circuit 11 includes a hydraulic pump 21 drivenby engine 5, an oil passage 22 connected with a discharge port ofhydraulic pump 21 to transmit (feed) a hydraulic fluid to primarychamber 2 c and secondary chamber 3 c, a pressure regulating valve 23arranged to regulate the discharge pressure from hydraulic pump 21 (thatis, the hydraulic pressure within oil passage 22), and a pressurereducing valve (a secondary pressure regulating valve) 24 arranged todecrease the hydraulic pressure supplied from oil passage 22 tosecondary chamber 3 c.

The hydraulic fluid within oil passage 22 is regulated to apredetermined line pressure PL by pressure regulator valve 23. Then,this line pressure PL of oil passage 22 is adjusted by pressure reducingvalve 24, and is supplied, as secondary pressure Psec, to secondarychamber 3 c. On the other hand, this line pressure PL is regulated by ashift control valve 25, and supplied, as primary pressure Ppri foracting on movable pulley 2 b of primary pulley 2, to primary chamber 2c.

Each of pressure regulator valve 23 and pressure reducing valve 24 is asolenoid valve. Pressure regulator valve 23 is arranged to regulate linepressure PL by driving duty to a solenoid 23 a. Pressure reducing valve24 is arranged to regulate secondary pressure Psec by driving duty to asolenoid 24 a. As shown in FIG. 4, an orifice 3 d is provided betweensecondary chamber 3 c and pressure reducing valve 24. Orifice 3 d isarranged to reduce (slow) discharge speed of the hydraulic fluid whenthe hydraulic fluid is discharged from secondary chamber 3 c by pressurereducing valve 24. Therefore, it is possible to prevent sudden decreaseof the secondary pressure (the secondary thrust), and to prevent theslippage of the belt.

Shift control valve 25 is arranged to be moved among a neutral position25 a, a pressure-increase position 25 b, and a pressure-decreaseposition 25 c. Shift control valve 25 supplies the hydraulic fluid tosecondary chamber 3 c at pressure-increase position 25 b to increase thehydraulic pressure, and drains the hydraulic fluid from secondarychamber 3 c at pressure-decrease position 25 c to decrease the hydraulicpressure. Shift control valve 25 is connected with an intermediateportion (a central portion) of a shift link (a servo link) 26 to switcha valve position among neutral position 25 a, pressure-increase position25 b, and pressure-decrease position 25 c. A step motor 27 is connectedwith one end of shift link 26, and serves as a shift actuator. Movablepulley 2 b of primary pulley 2 is connected with the other end of servolink 26. Shift control valve 25, shift link 26, and step motor 27 serveas a mechanical feedback system arranged to automatically adjust theactual pulley ratio to the target pulley ratio.

When step motor 27 is moved a step number STEP corresponding to thetarget pulley ratio, from a reference position to an operationalposition, shift link 26 is swung about the connection point betweenshift link 26 and movable pulley 2 b by this movement of step motor 27,and shift control valve 25 is moved from neutral position 25 a topressure-increase position 25 b or pressure-decrease position 25 c.Accordingly, primary pressure Ppri is increased by line pressure PLserving as the source pressure, or decreased by the discharge of thehydraulic fluid from a drain. Consequently, a pressure differencebetween primary pressure Ppri and secondary pressure Psec is varied,movable pulley 2 b of primary pulley 2 is moved to a positioncorresponding to the position of step motor 27, and movable pulley 3 aof secondary pulley 3 is moved in accordance with the movement ofmovable pulley 2 b of primary pulley 2. Thereby, shift operations suchas an upshift to the high pulley ratio and a downshift to the low pulleyratio are performed.

At this shift operation, movable pulley 2 b of primary pulley 2 ismoved, and the other end of shift link 26 which is connected withmovable pulley 2 b is swung about (on) the connection point between stepmotor 27 and shift link 26. When movable pulley 2 b of primary pulley 2is moved to a position (a target pulley ratio position) corresponding tothe position of step motor 27, shift link 26 returns shift regulatingvalve 25 from pressure-increase position 25 b or reducing pressureposition 25 c to neutral position 25 a. This mechanical feedback systemautomatically regulates the hydraulic pressure to adjust the actualpulley ratio to the target pulley ratio.

Transmission controller 12 (the control section) is configured to setthe solenoid driving duty of pressure regulator valve 23, the solenoiddriving duty of pressure reducing valve 24, and to control the drivingof step motor 27. As shown in FIG. 3, transmission controller 12 has apressure control section 12 a and shift control section 12 b each ofwhich serves as a functional element. An input side of pressure controlsection 12 a is connected with an input torque sensing section 19,primary pulley rotation sensor 13, secondary pulley rotation sensor 14,and shift control section 12 b. Pressure control section 12 a receivesan input torque information Ti (such as an engine rotational speed and afuel injection time period), primary pulley rotational speed Npri,secondary pulley rotational speed Nsec, and a shift speed informationdescribed later, and calculates (determines) target secondary pressurePtsec in accordance with input torque information Ti, primary pulleyrotational speed Npri, secondary pulley rotational speed Nsec, and theshift speed information. Then, pressure control section 12 a controlsthe solenoid driving duty of pressure regulator valve 23 and thesolenoid driving duty of pressure reducing valve 24 in accordance withtarget secondary pressure Ptsec, so as to regulate secondary pressurePsec supplied to secondary chamber 3 c.

Shift control section 12 b is connected with primary rotational speedsensor 13, secondary rotational speed sensor 14, a throttle openingsensor 17, a vehicle speed sensor 30, and a hydraulic fluid temperaturesensor 31, and receives primary pulley rotational speed Npri andsecondary pulley rotational speed Nsec. Shift control section 12 b setstarget pulley ratio IPt in accordance with primary pulley rotationalspeed Npri and secondary pulley rotational speed Nsec, to set drivingstep number STEP of step motor 27.

(control for the step motor) Hereinafter, the driving step numbercontrol operation of step motor 27 which is performed by shift controlsection 12 b will be illustrated. FIG. 1 is a block diagram forillustrating the control operation of step motor 27 which is performedby shift control section 12 b. As shown in FIG. 1, shift control section12 b includes a target pulley ratio setting section 100, a high speedshift judgment section (judgment section) 101, an actual pulley ratiocalculating section (actual pulley ratio sensing section) 102, a controlsection 103, and a command value conversion section 111 which serve asfunctional elements. Shift control section 12 b receives a vehicle speedV, a throttle opening TVO, primary pulley rotational speed Npri, andsecondary pulley rotational speed Nsec, and determines a targettransmission gear ratio command value, in accordance with vehicle speedV, throttle opening TVO, primary pulley rotational speed Npri, andsecondary pulley rotational speed Nsec. Shift control section 12 boutputs a driving step number command signal corresponding to the targettransmission gear ratio command value, to a motor driver 27 a configuredto control step motor 27.

Target pulley ratio setting section 100 receives throttle opening TVOand vehicle speed V, and sets target pulley ratio IPt in accordance withthrottle opening TVO and vehicle speed V, by a shift diagram based onthrottle opening TVO and vehicle speed V. High speed shift judgmentsection 101 receives vehicle speed V, an oil temperature OT, actualpulley ratio IPr, and target pulley ratio IPt. High speed shift judgmentsection 101 judges whether there is a request for a high speed shift(high speed movement) or not, in accordance with vehicle speed V, oiltemperature OT, actual pulley ratio IPr, and target pulley ratio IPt.High speed shift judgment section 101 selects, as a shift speed at theshift operation, a normal shift speed (a first speed) or a high shiftspeed (a second speed) faster than the normal shift speed. When highspeed shift judgment section 101 selects the shift at the first speed (anormal shift mode), high speed shift 2 q judgment section 101 controlsswitch P1 serving as a movement switching section provided in controlsection 103, to be connected with a 0 terminal. When high speed shiftjudgment section 101 selects the shift at the second speed (a high speedshift mode), high speed shift judgment section 101 controls switch P1 tobe connected with a 1 terminal. Moreover, high speed shift judgmentsection 101 is configured to output a control signal to pressure controlsection 12 a, and to control switching of switch P2 and switch P3provided in pressure control section 12 a as described later. Judgment(Control) conditions in high speed shift judgment section 101 andcontrol conditions of the switching of each of switches P1˜P3 will beillustrated later.

Command value conversion section 111 has a map based on the transmissiongear ratio and the position of step motor 27. Command value conversionsection 111 is configured to convert the transmission gear ratio commandvalue outputted from control section 103, to the driving step numbercommand signal of step motor 27. Control section 103 includes twocontrol circuits of a high speed shift control section 103 a and anormal control section 103 b, and a switch P1 arranged to switch theoutput of high speed shift control section 103 a and the output ofnormal control section 103 b. An output side of high speed shift controlsection 103 a is connected with the 1 terminal of switch P1. An outputside of normal section 103 b is connected with the 0 terminal of switchP1. That is, when high speed shift judgment section 101 selects thenormal shift mode, control section 103 outputs an output value of normalcontrol section 103 b. When high speed shift judgment section 101selects the high speed shift mode, control section 103 outputs an outputvalue of high speed shift control section 103 a.

Normal control section 103 b includes a time constant setting section104, a following (tracking) compensating section (compensator) 105, again calculating section 106, a first filter 107, a delay circuit 108,and a second filter 109. Normal control section 103 b is a feedbackcircuit using the transmission gear ratio command value (that is, thedriving command value of step motor 27) and actual pulley ratio IPrinputted from actual pulley ratio calculating section 102. Normalcontrol section 103 b calculates the driving command value of step motor27 at an every predetermined calculating cycle.

In normal control section 103 b, first, time constant setting section104 sets a time constant T relating to the shift speed. Followingcompensation section 105 receives time constant T and target pulleyratio IPt. Time constant T is set based on a map of throttle opening TVOand vehicle speed V, and difference between target pulley ratio IPt andactual pulley ratio IPr (that is, a shift width). This time constant mapis stored at each of shift operations such as the upshift, thedownshift, and the depression-induced downshift (a downshiftaccompanying the driver's depression).

Following compensation section 105 delays target pulley ratio IPt inaccordance with time constant T by the first-order delay, based ontarget pulley ratio IPr and time constant T, and calculates or computesa transient target pulley ratio IPtm. That is, transient target pulleyratio IPtm is set to increase linearly with the time, in considerationwith the delay of the response of the actual pulley ratio with respectto the transmission gear ratio command value. Besides, the differencebetween target pulley ratio IPt and transient target pulley ratio IPtmwhich is divided by time constant T is a target shift speed(IPt−Iptm)/T.

Actual pulley ratio calculation section 102 outputs a signal of actualpulley ratio IPr to gain calculation section 106 and first filter 107.Gain calculation section 106 outputs an F/B correction value which apredetermined gain is added to actual pulley ratio IPr. Transient targettransmission gear ratio IPtm outputted from following compensator 105 ismodified by subtracting the F/B correction value.

Each of first filter 107 and second filter 109 is a first-order delayfilter, and has a predetermined filter coefficient. That is, firstfilter 107 decreases a minute (minimal) variation (noise) of theinputted signal of actual pulley ratio IPr. First filter 107 decreasesfluctuation range (variation range) in a case in which actual pulleyratio IPr is suddenly varied, and outputs a signal value (an actualpulley ratio filter value) of this actual pulley ratio IPr with thedecreased variation width (fluctuation range). Second filter 109decreases noise and sudden variation of the transmission gear ratiocommand value calculated at the prior calculation circle, and outputs asignal value (a transmission gear ratio command filter value) of thistransmission gear ratio with the decreased fluctuation range.

Delay circuit 108 is a circuit in which an output signal is delayed by apredetermined time period (a predetermined calculation periodic number)with respect to an input signal. Delay circuit 108 outputs a signalvalue inputted before a predetermined calculation periodic number. Thetransient target transmission gear ratio is modified by subtracting adifference between the output value from first filter 107 and the outputvalue from delay circuit 108, and outputted as the transmission gearratio command value. Moreover, the difference between the output valuefrom first filter 107 and the output value from delay circuit 108 isinputted to a steady-state error section 110 of high speed shift controlsection 103 a described later, as a correction quantity for modifying asteady-state error in high speed shift control section 103 a.

In this way, normal control section 103 b performs a feedback control sothat actual pulley ratio IPr reaches target pulley ratio IPt at a shifttime period (the shift speed) set by time constant T. Next, high speedshift control section 103 a will be illustrated. High speed shiftcontrol section 103 a includes steady-state error correction section 110configured to output a correction quantity signal to a steady-stateerror of actual pulley ratio IPr with respect to the transmission gearratio command value. This correction quantity is inputted from normalcontrol section 103 b immediately before the switching to the high speedcontrol operation.

High speed shift control section 103 a does not perform the feedbackcontrol operation with respect to the inputted target pulley ratio IPr,and performs open-loop control operation. That is, the signal value oftarget pulley ratio IPr which is inputted from target pulley ratiosetting section 100 is modified by the output value from steady-stateerror correction section 110, and directly inputted to motor driver 27a. Motor driver 27 a drives (moves) step motor 27 to a positioncorresponding to the inputted target pulley ratio IPt.

(control for the secondary pressure) Hereinafter, control for thesecondary pressure which is performed in pressure control section 12 awill be illustrated. FIG. 5 is a block diagram for illustrating controlto determine target secondary pressure Ptsec in pressure control section12 a. As shown in FIG. 5, pressure control section 12 a includes atarget secondary pressure setting section 12 c serving as a functionalcomponent. Target secondary pressure setting section 12 c includes abase secondary pressure setting section 120, a centrifugal thrustcorrection section 121, a reduction rate limiter 123, a thrustdifference correction section 124, a first comparison section 125, and asecond comparison section 126. Target secondary pressure setting section12 c calculates (determines) target secondary pressure Ptsec by usingparameters A1˜A6 as described below.

Pressure control section 12 a includes a switch P2 and a switch P3 eachconfigured to perform the switching in response to a control signal fromhigh speed shift judgment section 101 of shift control section 12 b.Parameter A1 (a centrifugal force correction quantity A1) is acorrection quantity which corresponds to a centrifugal force, and whichcorresponds to a centrifugal thrust generated by the centrifugal forceof secondary pulley 3. Centrifugal force correction quantity A1 is setin accordance with secondary rotational speed Nsec.

Parameter A2 (a pump limit pressure A2) is a limit of pressure supply ofhydraulic pump 21 which varies in accordance with the output of engine5. Parameter 3 (a thrust difference correction quantity A3) is acorrection quantity for providing the difference of the thrust which isnecessary for performing the shift at the shift speed set by the mapcorresponding to target pulley ratio IPt, the actual pulley ratio andthe shift speed.

Parameter A4 (a lowest pressure or minimum pressure A4) is a mechanicalminimum limit pressure to judge whether the inputted value is equal toor greater than the minimum limit pressure capable of generating in amechanically stable state. That is, in a case in which the secondarypressure necessary for transmitting the torque is smaller than themechanical minimum limit pressure, the secondary pressure command valueis set to minimum pressure A4 as the minimum limit of the secondarypressure command value. Parameter A5 (a belt limit pressure A5) is asecondary pressure corresponding to a limit of strength of V-belt 4. Ina case in which the secondary pressure Psec exceeds this belt limitpressure A5, damage such as a rupture of V-belt 4 may be incurred.

Parameter A6 (a belt limit pressure excess correction quantity A6) is acorrection quantity which is added to belt limit pressure A5 when highspeed shift judgment section 101 controls switch P2 to be connected withthe 1 terminal in a case in which a predetermined condition as describedlater is satisfied (an excess hydraulic pressure mode). A change ratelimiter is configured to gradually increase or gradually decrease beltlimit pressure excess correction quantity A6 which is added to beltlimit pressure A5 (target secondary pressure Ptsec) for the correction.Accordingly, when the connection of switch P3 is switched, it ispossible to prevent sudden disappearance of belt limit pressure excesscorrection quantity A6 which is added to belt limit pressure A5, and toprevent sudden addition of belt limit pressure excess correctionquantity A6 to belt limit pressure A5. Therefore, it is possible toprevent the sudden variation of target secondary pressure Ptsec.

First, the control operation in the normal shift mode will beillustrated. In the normal shift mode, high speed shift judgment section101 controls switch P2 to be connected with the 0 terminal, and controlsswitch P3 to be connected with the 0 terminal. In pressure controlsection 12 a, first, base secondary pressure setting section 120 sets abase secondary pressure (a base secondary thrust) from the map based onthe inputted torque information Ti.

Then, centrifugal thrust correction section 121 modifies the basesecondary pressure determined in base secondary pressure setting section120, by subtracting centrifugal force correction quantity A1. That is,base secondary pressure setting section 120 and centrifugal thrustcorrection section 121 calculate secondary pressure Psec for obtaining aminimum thrust necessary for the torque transmission without incurringthe slippage of the belt.

Next, correction by reduction rate limiter 123 is performed. Reductionrate limiter 123 stores target secondary pressure Ptsec which iscalculated immediately before. Reduction rate limiter 123 is configuredto limit a reduction rate or a decreasing amplitude (range) to areference value when the inputted value is extremely small with respectto the stored target secondary pressure Ptsec (that is, when thereduction rate or the decreasing amplitude is equal to or greater than areference value). In a case in which the high value of secondarypressure Psec at the downshift is immediately decreased to the extremelow value of secondary pressure Psec at the upshift, the belt slippagetends to occur for the extreme decrease of secondary pressure Psec.However, reduction rate limiter 123 is arranged to limit the reductionrate or the decreasing amplitude to the reference value when thereduction rate or the decreasing range is equal to or greater than thereference value, and accordingly it is possible to suppress the suddendecrease of secondary pressure Psec, and thereby to prevent the beltslippage by the gentle variation in secondary pressure Psec.

Thrust difference correction section 124 modifies target secondarypressure Psec (the signal value from reduction rate limiter 123) byadding thrust difference correction quantity A3 so as to add thesecondary pressure necessary for generating the difference of the thrustnecessary for performing the shift at the desired shift speed. Firstcomparison section 125 is configured to compare minimum pressure A4 andthe value calculated by thrust difference correction section 124, and tooutput the greater one of these two values. Thereby, it is possible toprevent the secondary pressure command value from becoming smaller thanminimum pressure A4 which is the mechanical minimum limit.

Second comparison section 126 is configured to compare belt limitpressure A5 and the signal value determined in first comparison section125, and outputs, as target secondary pressure Ptsec, the smaller one ofbelt limit pressure A5 and the value calculated in first comparisonsection 125. Thereby, it is possible to prevent target secondarypressure Ptsec from becoming greater than the belt limitation secondarypressure. Next, the control operation in the high speed shift mode willbe illustrated. In the high speed control mode, switch P2 is connectedwith the 0 terminal, and switch P3 is connected with the 1 terminal.

In the high speed shift mode, switch P3 is connected with the 1terminal, and the control operations in base secondary pressure settingsection 120 and centrifugal thrust correction section 121 as describedabove are not performed. The smaller one of pump limit pressure A2 andbelt limit pressure A5 is inputted to reduction rate limiter 123.Besides, high speed shift judgment section 101 does not select the highspeed shift mode in a case in which the engine output is not apredetermined high output, as described later. Since the engine is inthe high output state when the shift mode is in the high speed shiftmode, pump limit pressure A2 usually becomes greater than belt limitpressure A5. Consequently, belt limit pressure A5 is inputted toreduction rate limiter 123.

Then, reduction rate limiter 123, thrust difference correction section124, first comparison section 125, and second comparison section 126perform the above mentioned control operations. Consequently, secondcomparison section 126 always outputs belt limit pressure A5. In thisway, in the high speed control mode, target secondary pressure Ptsec isset to the mechanical limit value (belt limit pressure A5), to providethe difference of the thrust for performing the shift (the downshift) atthe high shift speed.

Next, a control operation in the excess hydraulic pressure mode will beillustrated. In the excess hydraulic pressure mode, high speed shiftjudgment section 101 controls switch P2 to be connected with the 1terminal, and controls switch P3 to be connected with the 1 terminal. Inthe excess hydraulic pressure mode, switch P2 is connected with the 1terminal, and reduction rate limiter 123 receives the lower one of pumplimit pressure A2 and sum (an excess hydraulic pressure) of belt limitpressure A5 and belt limit pressure excess correction quantity A6. Sincein the excess hydraulic pressure mode the engine is in the high outputstate, pump limit pressure A2 is usually greater than the excesshydraulic pressure. Accordingly, the excess hydraulic pressure isinputted to reduction rate limiter 123.

Then, reduction rate limiter 123, thrust difference correction section124, first comparison section 125, and second comparison section 126perform the above-mentioned control operations. Accordingly, secondcomparison section 126 always outputs the excess hydraulic pressure. Inthis way, in the excess hydraulic pressure mode, target secondarypressure Ptsec is set to the excess hydraulic pressure which is the sumof the mechanical limit value (belt limit pressure A5) and belt limitpressure excess correction quantity A6, to provide the difference of thethrust for performing the shift (the downshift) at the high shift speed.In the excess hydraulic pressure mode, target secondary pressure Ptsecis set to the excess hydraulic pressure greater than belt limit pressureA5, and however the actual secondary pressure Psec does not reach thebelt limit secondary pressure as described later. Accordingly, thedamage such as the rupture of the V belt does not occur.

(judgment conditions of high speed shift judgment section) Next, thejudgment at high speed shift judgment section 101 and a switch startcondition of each of switches P1˜P3 shown in FIGS. 1 and 5 will beillustrated. FIG. 6 is a flow chart showing a control process performedby high speed shift judgment section 101. As shown in FIG. 6, high speedshift judgment section 101 selects the high speed shift mode when theconditions of step S100˜step S130 are satisfied, and the shift at thesecond speed is performed.

A first condition shown in step S100 is a condition of the engine output(engine load state). At step S100, high speed shift judgment section 101judges whether throttle opening TVO is within a predetermined region ofTVO_(L)≦TVO≦TVO_(H) or not. When the answer of step S100 is affirmative(YES), the process proceeds to step S110. When the answer of step S100is negative (NO), the process proceeds to the return. In this condition,when throttle opening TVO is smaller than the reference level TVO_(L),it is possible to judge that the engine is a low load state, and thatthere is no acceleration request. On the other hand, when throttleopening TVO is extremely large, the significant downshift is notperformed.

A second condition shown in step S110 is a condition of the downshiftthat deviation (error) ΔIP between the inputted target pulley ratio IPrand actual pulley ratio IPr (=IPt−IPr, ΔIP>0) is equal to or greaterthan a predetermined shift width ipt₀. When deviation ΔIP is equal to orgreater than the predetermined shift width ipt₀, the process proceeds tostep S120. When the deviation ΔIP is not equal to or greater than thepredetermined shift width ipt₀, the process returns to the return. In acase in which the driver requests the sudden acceleration, theaccelerator pedal is depressed, and target pulley ratio IPt isimmediately increased to the downshift side, so that deviation ΔIPbetween target pulley ratio IPt and actual pulley ratio IPr isincreased. Accordingly, it is possible to judge that there is necessaryto perform the depression-induced downshift control that the driverrequests the sudden acceleration when deviation ΔIP is equal to orgreater than the predetermined shift width ipt₀. Besides, in a case inwhich the shift width is small, the high shift speed is not requested,and switch P1 is set to the 0 position. Normal control section 103 bperforms the shift operation at the first speed.

A third condition at step S120 is a condition that vehicle speed V is ina predetermined range (V_(L)≦V≦V_(H)). When the vehicle speed V is inthe predetermined range of V_(L)≦V≦V_(H), the process proceeds to stepS130. When vehicle speed V is not in the predetermined range ofV_(L)≦V≦V_(H), the process proceeds to the return. In each of pulleys 2and 3, when the shift speed per the pulley rotational speed (that is,corresponding to a stroke amount of the movable pulley 2 b per onerotation of the pulley) is increased, and the belt slippage tends tooccur. Accordingly, it is necessary to increase the thrust applied toeach of the pulleys 2 and 3, to the vicinity of the upper limit. In thisstate, even if the control operation of the high speed shift mode isperformed, it is not possible to attain the practical effect, andfurther the belt slippage may be incurred. Accordingly, at the lowvehicle speed that vehicle speed V is lower than the predeterminedvehicle speed (the reference vehicle speed) V_(L), the control operationof the high speed shift mode is not performed. On the other hand, at thehigh vehicle speed that vehicle speed V is greater than thepredetermined vehicle speed V_(H), there is no need that the shift speedis set to the high speed, and accordingly the high speed mode is notselected.

A fourth condition at step S130 is a condition that temperature OT ofthe hydraulic fluid supplied to the hydraulic system is in apredetermined range of OT_(L)≦OT≦OT_(H). When temperature OT of thehydraulic fluid is in the predetermined range of OT_(L)≦OT≦OT_(H), theprocess proceeds to step S140. When temperature OT of the hydraulicfluid is not in the predetermined range of OT_(L)≦OT≦OT_(H), the processproceeds to the return. In the case of the high temperature of thehydraulic fluid, the discharge quantity from the pump is decreased, andthe belt slippage may be incurred for the deficiency of the hydraulicpressure supplied to each of pulleys 2 and 3. In the case of the lowtemperature of the hydraulic fluid, responsiveness of the hydraulicfluid is poor, and the belt slippage may be incurred in the case of thedeficiency of the hydraulic pressure supplied to each of pulleys 2 and3.

When the conditions of step S100˜step S130 are satisfied, at step S140,high speed shift judgment section 101 controls switch P1 to be connectedwith the 1 terminal, and controls switch P3 to be connected with the 1terminal. That is, high speed shift judgment section 101 judges thatthere is the high speed shift request, and selects the high speed shiftmode. High speed shift control section 103 a of control section 103starts to control the transmission gear ratio command value (that is,the driving step number command signal of step motor 27) by theopen-loop control based on target pulley ratio IPr. Moreover, pressurecontrol section 12 a sets target secondary pressure Ptsec to belt limitpressure A5, and produces the thrust necessary for the shift at the highspeed.

In a case in which the high shift speed mode is selected at step S140,step S150 judges whether deviation ΔIP is equal to or greater than apredetermined shift width ipt₁ or not. This shift width ipt₁ is set to avalue greater than shift width ipt₀ at step S110. When deviation ΔIP isequal to or greater than the predetermined shift width ipt₁, the processproceeds to step S160. At step S160, high speed shift judgment section101 controls switch P2 to be connected with the 1 terminal. That is,high speed shift judgment section 101 selects the excess hydraulicpressure mode, and sets target secondary pressure Ptsec to the excesshydraulic pressure.

In the excess hydraulic pressure mode, target secondary pressure Ptsecis set to the value greater than the belt limit pressure as mentionedabove, and this reason will be illustrated below. As mentioned above,orifice 3 d is provided in the oil passage in the vicinity of secondarychamber 3 c. Accordingly, it is possible to prevent the sudden decreasein the secondary pressure when target secondary pressure Ptsec isimmediately set to a small value in a case in which the transmissiongear ratio is changed to the high side. Consequently, it is possible toprevent the actual secondary pressure from decreasing than targetsecondary pressure Ptsec, and thereby to prevent the belt slippage.

As mentioned above, orifice 3 d is provided between secondary chamber 3c and pressure reducing valve 24 as shown in FIG. 4. In a case ofincreasing the secondary pressure, the pressure between pressurereducing valve 24 and orifice 3 d is rapidly increased, and meanwhilethe pressure between secondary chamber 3 c and orifice 3 d is slackly(slowly) increased. Consequently, the pressure between secondary chamber3 c and orifice 3 d is in the low pressure state, even when the pressurebetween pressure reducing valve 24 and orifice 3 d is in the highpressure state. However, hydraulic pressure sensor 15 for sensing thissecondary pressure is provided between orifice 3 d and pressure reducingvalve 24 for the space limitations, and the output value of hydraulicpressure sensor 15 shows a value greater than the actual pressure ofsecondary chamber 3 c. Accordingly, in a case in which the feedbackcontrol of the secondary pressure is performed in accordance with thesensed value of hydraulic pressure sensor 15, it is judged that thesecondary pressure reaches the target value by judging the sensed value,even when the actual secondary pressure is low. Consequently, thecontrol shifted to the low pressure side is performed.

Accordingly, when a deviation (a secondary pressure deviation) betweenthe sensed value and the actual value of the secondary pressure is equalto or greater than a reference in a case in which the secondary pressureis rapidly increased, target secondary pressure Ptsec is modified byadding the predetermined quantity A6 corresponding to this deviation.Since target secondary pressure Ptsec is set to the belt limit pressure,target secondary pressure Ptsec which is modified by adding thepredetermined quantity A6 exceeds the belt limit pressure. Even whentarget secondary pressure Ptsec is set greater than the predeterminedbelt limit pressure, belt limit pressure excess correction quantity A6is set to the appropriate value, and actual secondary pressure Psec doesnot exceed the belt limit pressure. Moreover, it is possible to rapidlyincrease actual secondary pressure Psec, and to achieve the rapid shiftdown.

Step S150 judges whether deviation ΔIP is equal to or greater than thepredetermined shift width ipt₁ or not. That is, step S150 judges whetherthe secondary pressure deviation becomes large (a large value largerthan a reference value determined, in advance, by an experiment and soon) or not. When deviation ΔIP becomes equal to or greater than thepredetermined shift width ipt₁, step S150 judges that the secondarypressure deviation is large. At step S160, the control operation of theexcess hydraulic pressure mode is performed. When deviation ΔIP issmaller than shift width, it is judged that the secondary pressuredeviation is not large, and the excess hydraulic pressure mode is notselected.

In a case in which the control operation of the excess hydraulicpressure mode is performed at step S160, step S170 judges whetherdeviation ΔIP between target pulley ratio IPt and actual pulley ratioIPr is equal to or smaller than the predetermined shift width ipt₂. Thepredetermined shift width ipt₂ is a threshold value for judging that thedifference between target pulley ratio IPt and actual pulley ratio IPris small, and that the shift is shortly terminated. Shift width ipt₂ isset to a minute value smaller than shift widths ipt₀ and ipt₁.

When the difference between target pulley ratio IPt and actual pulleyratio IPr is greater than the predetermined shift width ipt₂, theprocess returns to step S160. The excess hydraulic pressure mode iscontinued until the difference between target pulley ratio IPr andactual pulley ratio IPr becomes equal to or smaller than thepredetermined shift width ipt₂. When the difference between targetpulley ratio IPt and actual pulley ratio IPr becomes equal to or smallerthan shift width ipt₂, the process proceeds to step S180. High speedshift judgment section 101 controls switch P2 to be connected with the 0terminal, and terminates the excess hydraulic pressure mode.

As mentioned above, in this state, when switch P2 is connected with the0 terminal in FIG. 5, the input of belt limit pressure excess correctionquantity A6 added to belt limit pressure A5 is interrupted. The changerate limiter gradually decreases the correction quantity which is addedto belt limit pressure A5. At step S190, deviation ΔIP and apredetermined shift width ipt₃ serving as the predetermined referencevalue are compared in a magnitude relation. When deviation ΔIP isgreater than the predetermined shift width ipt₃, the process returns tostep S140. The high speed shift mode is continued until deviation ΔIPbecomes equal to or smaller than the predetermined shift width ipt₃.When deviation ΔIP becomes equal to or smaller than the predeterminedshift width ipt₃, the process proceeds to step S200. High speed shiftjudgment section 101 controls switch P1 to be connected with the 0terminal, controls switch P2 to be connected with the 0 terminal, andterminates the high speed shift mode. Shift width ipt₃ is set smallerthan shift width ipt₂ because the change rate limiter graduallydecreases the correction quantity which is added to belt limit pressureA5, even though the excess hydraulic pressure mode is terminated at stepS180.

In the control apparatus for the continuously-variable automatictransmission according to the present invention, normal control section103 b performs the feedback control for the transmission gear ratiocommand value (the driving step number command signal of step motor 27)based on target pulley ratio IPt, at the normal shift. Thereby, it ispossible to surely adjust actual pulley ratio IPr to target pulley ratioIPt. In this feedback control operation, following compensation section105 linearly increases the transmission gear ratio command value inaccordance with time constant T corresponding to the shift speed (thefirst speed), in consideration with the variation characteristic inwhich actual pulley ratio IPr is linearly varied with respect to thetransmission gear ratio command value. Accordingly, it is possible torapidly adjust actual pulley ratio IPr to target pulley ratio IPt, andto decrease the deviation between the transmission gear ratio commandvalue and the actual pulley ratio IPr at the shift operation. Therefore,it is possible to decrease overshoot of actual pulley ratio IPr by theintegral control.

Moreover, in a case of requesting a high responsiveness of the shift atthe depression-induced downshift at the high-speed running, high speedshift judgment section 101 selects the high speed shift mode, andperforms the shift at the shift speed larger than the shift speed in thenormal condition. In this high speed shift mode, high speed shiftcontrol section 103 a performs the open-loop control of the transmissiongear ratio command value based on target pulley ratio IPt. Thereby, itis possible to suppress the overshoot of the transmission gear ratiowhich is incurred by the integral control when the feedback control isperformed, since the variation characteristic of actual pulley ratio IPris not the linear variation at the high shift speed (see FIG. 7). Inthis open-loop control, steady-state error correction section 110modifies the steady-state error of the correction value by thesteady-state error correction quantity inputted immediately beforeswitching from the normal shift mode to the high speed shift mode.Accordingly, it is possible to surely shift the actual pulley ratio totarget pulley ratio IPt.

Moreover, at the high speed shift mode, target secondary pressure Ptsecis set to belt limit pressure A5. In this state, when deviation ΔIPbecomes equal to or greater than the predetermined shift width ipt₁,target secondary pressure Ptsec is set to the sum of belt limit pressureA5 and belt limit pressure excess correction quantity A6. Accordingly,it is possible to keep actual secondary pressure Psec to the vicinity ofthe belt limit pressure, even when the orifice suppresses the increasingof actual secondary pressure Psec at the shift operation at the highspeed. Thereby, it is possible to keep the difference of the thrustnecessary for performing the shift operation at the high speed.Moreover, actual primary pressure Ppri is increased when actualsecondary pressure Psec is increased (in the high pressure state), andit is possible to prevent the slippage of the belt of primary pulley 2at the shift operation performed at the high speed.

In the high speed shift mode, when deviation ΔIP is equal to or greaterthan the predetermined shift width ipt₁ and the actual shift speed islarge, target secondary pressure Ptsec is set to the excess hydraulicpressure of the sum of belt limit pressure A5 and belt limit pressureexcess correction quantity A6. Accordingly, it is possible to hold thehydraulic pressure within secondary chamber 3 c to the vicinity of thebelt limit pressure, even when the detection error of the sensed actualsecondary pressure Psec with respect to the actual secondary pressure isincurred. Accordingly, it is possible to provide the difference of thethrust necessary for performing the high speed shift, and to prevent thedecrease in the secondary pressure for the detection error. Therefore,it is possible to decrease primary pressure Ppri with secondary pressurePsec, and to surely decrease the belt slippage.

In the control apparatus according to the present invention, when thecontroller judges that there is the high speed shift request, targetsecondary pressure Ptsec is set to the belt limit pressure or the excesshydraulic pressure greater than the belt limit pressure. The setting ofsecondary pressure Ptsec is not limited to this manner. For example,time constant T adjusted in accordance with a desired shift speed is setto perform the shift at the second speed, and target secondary pressurePtsec is set by the conventional manner.

Moreover, the judgment (control) conditions at high speed shift judgmentsection 101 are not limited to the above described conditions. In thecontrol apparatus according to the embodiments, when the conditions ofstep S100˜step S130 as shown in FIG. 6 are satisfied, the controllerjudges that there is the high speed operation request. However, forexample, the only condition of deviation ΔIP of step S110 may beemployed. Moreover, it is optional to employ, as the engine loadcondition of step S100, a condition that accelerator pedal opening (APO)is in a predetermined region, instead of throttle opening TVO.Furthermore, it is optional to switch to the normal shift mode bytime-out measured by a timer in a case in which the high speed shiftmode continues during a predetermined time period, for surely preventingthe belt slippage, in addition to the conditions of step S100˜step S130.

In the control apparatus according to the embodiment of the presentinvention, the conditions of the start of the excess hydraulic pressuremode are the condition that the high speed shift mode is selected toadjust the shift speed to the high speed, and the condition deviationΔIP is equal to or greater than the predetermined shift width ipt₁.Additionally, it is optional to add a condition that the actual shiftspeed is equal to or greater than a predetermined speed. In this case,it is optional to omit the condition that deviation ΔIP is equal to orgreater than the predetermined shift width ipt₁. Thereby, only when theactual shift speed is equal to or greater than the predetermined speedand the pressure difference between the both sides of orifice 3 d isequal to or greater than a constant value, the excess hydraulic pressuremode is selected. Accordingly, it is possible to keep the pressurewithin secondary chamber 3 c to the vicinity of the belt limit pressurewithout exceeding belt limit pressure A5. Therefore, it is possible toprevent the damage of the belt by the excessive secondary pressure Psec,and to surely prevent the belt slippage by the decrease in secondarypressure Psec.

In the control apparatus according to the embodiment of the presentinvention, when the controller judges that there is the high speed shiftrequest, target secondary pressure Ptsec is set to the belt limitpressure or the excess hydraulic pressure larger than the belt limitpressure. The setting of target secondary pressure Ptsec is not limitedto the above-mentioned manner. For example, time constant T adjusted inaccordance with the desired shift speed is set to perform the shift atthe second speed, and target secondary pressure Ptsec is set by theconventional manner. Then, in this state, when the above-mentionedcondition (the excess hydraulic pressure mode start condition) issatisfied, it is optional to further modify target secondary pressurePtsec set by the conventional manner, by adding the predeterminedcorrection quantity. Thereby, it is possible to prevent the adverseeffect of the suppression of the pressure increase at the high speedshift which is incurred by the orifice, and to prevent the actualpressure within secondary chamber 3 c from extremely decreasing withrespect to the set target secondary pressure Ptsec.

Moreover, the judgment conditions at high speed shift judgment section101 are not limited to the conditions of the control apparatus accordingto the embodiments. In the control apparatus according to theembodiments, when the conditions of step S100˜step S130 as shown in FIG.6 are satisfied, the controller judges that there is the high speedoperation request. Moreover, it is optional to add a condition thatprimary pulley rotational speed Npri is within the predetermined rangeto surely prevent the belt slippage, in addition to the conditions ofstep S100˜step S130. Moreover, it is optional to switch to the normalshift mode by time-out measured by a timer in a case in which the highspeed shift mode continues during a predetermined time period, forsurely preventing the belt slippage, in addition to the conditions ofstep S100˜step S130.

The control apparatus for the transmission according to the embodimentof the present invention includes a primary pulley including a movablepulley, the primary pulley being connected with an input, a secondarypulley including a movable pulley, the secondary pulley being connectedwith an output, a belt wound around the primary pulley and the secondarypulley, a shift control valve configured to regulate a hydraulicpressure acting on the movable pulley of the primary pulley, and tocontrol a target pulley ratio between the primary pulley and thesecondary pulley, a secondary pressure regulating valve configured toregulate a secondary hydraulic pressure acting on the movable pulley ofthe secondary pulley, and to regulate an engagement pressure between thebelt and each of the primary pulley and the secondary pulley, an orificedisposed in an oil passage between the movable pulley of the secondarypulley and the secondary pressure regulating valve, a hydraulic pressuresensor disposed between the secondary pressure regulating valve and theorifice in the oil passage, and configured to sense an actual secondarypressure, and a control section including a target secondary pressuresetting section configured to set the target secondary pressure within astrength limit of the belt so as to prevent a slippage between the beltand each of the primary pulley and the secondary pulley, and anoperation switching section configured to switch a shift operation froma normal speed to a high speed higher than the normal speed when apredetermined condition is satisfied, the control section beingconfigured to control the secondary pressure regulating valve by afeedback control based on the target secondary pressure and the actualsecondary pressure sensed by the hydraulic pressure sensor. The targetsecondary pressure setting section is configured to modify the targetsecondary pressure by adding a predetermined quantity when a correctioninitiation condition is satisfied, the condition initiation conditionincluding a first condition that the shift operation is performed at ahigh speed by switching of the operation switching section.

In the case of performing the shift at the high speed, it is necessaryto increase the target secondary pressure for preventing the beltslippage. The orifice is provided in the oil passage between the movablepulley (that hydraulic chamber) of the secondary pulley and thesecondary pressure regulating valve. In the case in which the hydraulicpressure sensor is provided between the orifice of the oil passage andthe secondary pressure regulating valve, the hydraulic pressure betweenthe secondary pressure regulating valve and the orifice is increased,and is sensed by the hydraulic pressure sensor.

However, the hydraulic pressure of the movable pulley (the hydraulicchamber) of the secondary pulley is not immediately increased.Accordingly, the hydraulic pressure sensor outputs the value larger thanthe actual secondary pressure. In the feedback control of the secondarypressure based on the output from the hydraulic pressure sensor, thecontroller performs control operations, provided that the actualsecondary pressure is increased to the target secondary pressure, thoughthe actual secondary pressure is not increased to the target secondarypressure. The actual secondary pressure is deficient, and accordinglythe actual primary pressure (the hydraulic pressure supplied to themovable pulley of the primary pulley) is lowered. Consequently, the beltslippage may be incurred.

In the illustrated example, in this case, the target secondary pressureis modified by adding the correction quantity, and it is possible toincrease the actual secondary pressure to the inherent target secondarypressure (the target secondary pressure without adding the correctionquantity), and to prevent the belt slippage.

In the control apparatus according to the embodiment, the targetsecondary pressure setting section is configured to set a base targetsecondary pressure based on the target pulley ratio and the actualpulley ratio, to modify the base target secondary pressure by asecondary centrifugal thrust, and to modify the base target secondarypressure to the target secondary pressure by adding the predeterminedquantity when the correction initiation condition is satisfied.

Accordingly, it is possible to adequately control the actual secondarypressure in consideration with the centrifugal thrust generated by thecentrifugal force.

In the control apparatus according to the embodiment, the targetsecondary pressure setting section is configured to limit a change rateof the predetermined quantity.

Accordingly, it is possible to prevent the rapid decrease in thecorrection quantity with respect to the target secondary pressure.Accordingly, it is possible to prevent the excess decrease in thesecondary pressure generated by the rapid decrease in the targetsecondary pressure, and to prevent the belt slippage.

In the control apparatus according to the embodiment, the targetsecondary pressure setting section is configured to terminate thecorrection of the target secondary pressure when a correctiontermination condition is satisfied during the correction of the targetsecondary pressure.

Moreover, the control apparatus terminates the correction that thecorrection quantity is added to the target secondary pressure when thepredetermined correction termination condition is satisfied. Therefore,it is possible to prevent the excess increase in the secondary pressure,and to surely prevent the damage of the belt which is incurred by theexcess pressure.

In the control apparatus according to the embodiment, the targetsecondary pressure setting section is configured to set the targetsecondary pressure to a belt strength limit pressure when the operationswitching section switches the shift operation to the high speed, and tomodify the target secondary pressure set to the belt strength limitationpressure, by adding the predetermined quantity when the correctioninitiation condition is satisfied.

In the control apparatus according to the embodiment of the presentinvention, the target secondary pressure is set to the belt strengthlimitation value when the shift operation is switched to the high speedoperation. Accordingly, it is possible to prevent the decrease in thesecondary pressure at the high speed shift, and to prevent the beltslippage. Moreover, in this state, the target secondary pressure ismodified by adding the correction quantity when the correctionconditions are satisfied. Accordingly, it is possible to prevent theeffect of the suppression of the secondary pressure which is caused bythe orifice, and to keep the secondary pressure in the high pressurestate. Therefore, it is possible to surely prevent the decrease in thesecondary pressure at the shift performed at the high speed, and toprevent the belt slippage.

In the control apparatus according to the embodiment, the correctioninitiation condition includes a second condition that the shift speed isgreater than a predetermined speed, and that a deviation between thetarget secondary pressure and the actual secondary pressure is equal toor greater than a first predetermined value (ipt₁).

There are the conditions that the shift speed is equal to or greaterthan the predetermined speed, the condition that the deviation betweenthe actual value of the secondary pressure and the value sensed by thehydraulic pressure sensor is equal to or greater than the predeterminedvalue by the effect of the orifice at the shift. Accordingly, even whenthe target secondary pressure is modified by adding the correctionquantity, the correction quantity is absorbed by the deviation betweenthe actual value of the secondary pressure and the value sensed by thehydraulic pressure sensor. Therefore, it is possible to prevent theexcess increase in the actual value of the secondary pressure.

In the control apparatus according to the embodiment, the controlsection is configured to gradually increase the additional correctionquantity at a start of the correction of the target secondary pressure.

At the start of the correction of the target secondary pressure byadding the correction quantity, the correction quantity is graduallyincreased to the predetermined value. At the shift, the actual shiftspeed is increased, the deviation between the actual value of thesecondary pressure and the value sensed by the hydraulic pressure sensoris gradually increased by the effect of the orifice, and the correctionquantity is increased correspondingly. Accordingly, when the targetsecondary pressure is modified by adding the correction quantity, thecorrection quantity is absorbed by the deviation between the actualvalue of the secondary pressure and the value sensed by the hydraulicpressure sensor. Therefore, it is possible to prevent the excessincrease in the actual value of the secondary pressure.

In the control apparatus according to the embodiment, the controlapparatus further includes a step motor arranged to be moved to aposition in accordance with the target pulley ratio between the primarypulley and the secondary pulley, a servo link connected with the stepmotor, the movable pulley of the primary pulley, and the shift controlvalve, and arranged to move the movable pulley of the primary pulleythrough the shift control valve in accordance with the position of thestep motor, an actual pulley ratio sensing section configured to sensean actual pulley ratio between the primary pulley and the secondarypulley; and the control section includes a target pulley ratio settingsection configured to set the target pulley ratio, a normal controlsection configured to actuate the step motor at a first speed by using afeedback control operation including an integral control in accordancewith the target pulley ratio and the actual pulley ratio, a high speedcontrol section configured to actuate the step motor at a second speedhigher than the first speed by using an open loop control operationbased on the target pulley ratio, a judgment section configured to judgewhether there is a high speed operation request to perform the shiftoperation at the high speed, and the operation switching sectionconfigured to select a control operation performed by the normal controlsection at a normal condition, and to switch to a control operationperformed by the high speed control section when a switch startcondition is satisfied, the switch start condition including a conditionthat there is the high speed operation request judged by the judgmentsection.

In the control apparatus according to the embodiment of the presentinvention, when there is not the high speed shift request, the shiftoperation is performed at the normal speed (the first speed) within theconstant speed. Accordingly, it is possible to appropriately perform thefeedback control by using the simple filter for the feedback. On theother hand, when there is the high speed shift request, the shiftoperation is performed at the high speed (the second speed) greater thanthe constant speed. In this case, it is difficult to perform theappropriate control by using the simple filter for the feedback.However, it is possible to perform the rapid shift control by using theopen-loop control.

In the control apparatus according to the embodiment, the judgmentsection judges that there is the high speed operation request when thedeviation between the target pulley ratio set by the target pulley ratiosetting section and the actual pulley ratio sensed by the actual pulleyratio sensing section is equal to or greater than a second predeterminedvalue.

Accordingly, it is possible to surely judge that there is the high speedshift request and the shift width is equal to or greater than thepredetermined reference value, from deviation ΔIP between target pulleyratio IPt and actual pulley ratio IPr (=IPt−IPr).

In the control apparatus according to the embodiment, the switch startcondition includes a first switch start condition that a vehicle speedis equal to or greater than a predetermined vehicle speed, and a secondswitch start condition that a load condition of an engine connected withthe primary pulley is equal to or greater than a predetermined load.

Accordingly, it is possible to surely prevent the belt slippage whichtends to occur when the shift is performed at the high speed at the lowrunning speed. Furthermore, it is possible to surely judge that there isthe high speed operation request and the acceleration request, from theload condition of the engine connected with the rotation input side.

In the control apparatus according to the embodiment, the operationswitching section is arranged to switch from the control operation ofthe high speed control section to the control operation of the normalcontrol section when the deviation between the target pulley ratio setby the target pulley ratio setting section and the actual pulley ratiosensed by the actual pulley ratio sensing section becomes equal to orsmaller than a third predetermined value.

In the illustrated example, when the shift at the second speed isshortly terminated, the shift speed is varied to the first speed smallerthan the second speed. Accordingly, the transmission gear ratio does notexceed target pulley ratio ipt by the shift operation at the high speed,and it is possible to perform the smooth shift control.

In the control apparatus according to the embodiment, the signalprocessing circuit of the normal control section includes a compensatorconfigured to compensate a response delay of the step motor, and to havea time constant set in accordance with the first speed.

In the illustrated example, the signal processing circuit of the normalcontrol section is provided with the compensator configured tocompensate the response delay of the step motor. The compensator isprovided with the time constant set in accordance with the first speed.The compensator sets the target pulley ratio which is linearly increasedin accordance with the time constant set in accordance with the shiftspeed request. Accordingly, it is possible to decrease the deviationbetween the target pulley ratio and the actual pulley ratio ipr by theresponse delay of actual pulley ratio ipr. Therefore, it is possible todecrease the overshoot of actual pulley ratio ipr, and to perform thesmooth shift by the improvement of the responsiveness of actual pulleyratio ipr.

This application is based on a prior Japanese Patent Application No.2005-317644. The entire contents of the Japanese Patent Application No.2005-317644 with a filing date of Oct. 31, 2005 are hereby incorporatedby reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

What is claimed is:
 1. A control apparatus for an automatic transmissionof a vehicle, the control apparatus comprising: a primary pulleyincluding a movable pulley, the primary pulley being connected with aninput; a secondary pulley including a movable pulley, the secondarypulley being connected with an output; a belt wound around the primarypulley and the secondary pulley; a shift control valve configured toregulate a hydraulic pressure of a hydraulic fluid which varies a groovewidth of the movable pulley of the primary pulley, and to control atarget pulley ratio between the primary pulley and the secondary pulley;a secondary pressure regulating valve configured to regulate a secondarypressure of a hydraulic fluid which varies a groove width of the movablepulley of the secondary pulley, and to regulate an engagement pressurebetween the belt and each of the primary pulley and the secondarypulley; an orifice disposed in an oil passage which is located betweenthe movable pulley of the secondary pulley and the secondary pressureregulating valve, wherein the oil passage is connected to a feedbackhydraulic passage, wherein the orifice is arranged to restrict a flow ofthe hydraulic fluid between the movable pulley of the secondary pulleyand the secondary pressure regulation valve; a hydraulic pressure sensordisposed between the secondary pressure regulating valve and the orificedisposed in the oil passage, and configured to sense the secondarypressure; and a control section including a target secondary pressuresetting section configured to set a target secondary pressure within astrength limit of the belt so as to prevent a slippage between the beltand each of the primary pulley and the secondary pulley, and anoperation switching section configured to switch a shift operation froma normal speed to a high speed higher than the normal speed when apredetermined condition is satisfied, the control section beingconfigured to control the secondary pressure regulating valve by afeedback control based on the target secondary pressure and thesecondary pressure sensed by the hydraulic pressure sensor, wherein thetarget secondary pressure setting section is configured to modify thetarget secondary pressure by adding a predetermined quantity when acorrection initiation condition is satisfied, the correction initiationcondition including a first condition that the shift operation isperformed at a high speed by switching of the operation switchingsection.
 2. The control apparatus as claimed in claim 1, wherein thetarget secondary pressure setting section is configured to set a basetarget secondary pressure based on the target pulley ratio and an actualpulley ratio, to modify the base target secondary pressure by asecondary centrifugal thrust, and to modify the base target secondarypressure to the target secondary pressure by adding the predeterminedquantity when the correction initiation condition is satisfied.
 3. Thecontrol apparatus as claimed in claim 1, wherein the target secondarypressure setting section is configured to limit a change rate of thepredetermined quantity.
 4. The control apparatus as claimed in claim 1,wherein the target secondary pressure setting section is configured toterminate correction of the target secondary pressure when a correctiontermination condition is satisfied during correction of the targetsecondary pressure.
 5. The control apparatus as claimed in claim 1,wherein the target secondary pressure setting section is configured toset the target secondary pressure to a belt strength limit pressure whenthe operation switching section switches the shift operation to the highspeed, and to modify the target secondary pressure set to the beltstrength limitation pressure, by adding the predetermined quantity whenthe correction initiation condition is satisfied.
 6. The controlapparatus as claimed in claim 1, wherein the correction initiationcondition includes a second condition that the shift speed is greaterthan a predetermined speed, and that a deviation between the targetsecondary pressure and the secondary pressure is equal to or greaterthan a first predetermined value.
 7. The control apparatus as claimed inclaim 1, wherein the oil passage is located between the movable pulleyof the secondary pulley and the feedback hydraulic passage which extendsfrom the secondary pressure regulating valve.
 8. The control apparatusas claimed in claim 6, wherein the control section is configured togradually increase a quantity added to the target secondary pressure ata start of correction of the target secondary pressure.
 9. The controlapparatus as claimed in claim 8, wherein: the control apparatus furthercomprises a step motor arranged to be moved to a position in accordancewith the target pulley ratio between the primary pulley and thesecondary pulley, a servo link connected with the step motor, themovable pulley of the primary pulley, and the shift control valve, andarranged to move the movable pulley of the primary pulley through theshift control valve in accordance with the position of the step motor,an actual pulley ratio sensing section configured to sense an actualpulley ratio between the primary pulley and the secondary pulley; andthe control section includes a target pulley ratio setting sectionconfigured to set the target pulley ratio, a normal control sectionconfigured to actuate the step motor at a first speed by using afeedback control operation including an integral control in accordancewith the target pulley ratio and the actual pulley ratio, a high speedcontrol section configured to actuate the step motor at a second speedhigher than the first speed by using an open loop control operationbased on the target pulley ratio, a judgment section configured to judgewhether there is a high speed operation request to perform the shiftoperation at the high speed, and the operation switching sectionconfigured to select a control operation performed by the normal controlsection at a normal condition, and to switch to a control operationperformed by the high speed control section when a switch startcondition is satisfied, the switch start condition including a conditionthat there is the high speed operation request judged by the judgmentsection.
 10. The control apparatus as claimed in claim 8, wherein thenormal control section includes a compensator configured to compensate aresponse delay of the step motor, and to have a time constant set inaccordance with the first speed.
 11. The control apparatus as claimed inclaim 9, wherein the judgment section judges that there is the highspeed operation request when the deviation between the target pulleyratio set by the target pulley ratio setting section and the actualpulley ratio sensed by the actual pulley ratio sensing section is equalto or greater than a second predetermined value.
 12. The controlapparatus as claimed in claim 9, wherein the switch start conditionincludes a first switch start condition that a vehicle speed is equal toor greater than a predetermined vehicle speed, and a second switch startcondition that a load of an engine connected with the primary pulley isequal to or greater than a predetermined load.
 13. The control apparatusas claimed in claim 9, wherein the operation switching section isarranged to switch from the control operation of the high speed controlsection to the control operation of the normal control section when thedeviation between the target pulley ratio set by the target pulley ratiosetting section and the actual pulley ratio sensed by the actual pulleyratio sensing section becomes equal to or smaller than a thirdpredetermined value.
 14. A control method for an automatic transmissionof a vehicle including a primary pulley including a movable pulley, theprimary pulley being connected with an input, a secondary pulleyincluding a movable pulley, the secondary pulley being connected with anoutput, a belt wound around the primary pulley and the secondary pulley,a shift control valve configured to regulate a hydraulic pressure of ahydraulic fluid which varies a groove width of the movable pulley of theprimary pulley, and to control a target pulley ratio between the primarypulley and the secondary pulley, a secondary pressure regulating valveconfigured to regulate a secondary pressure of a hydraulic fluid whichvaries a groove width of the movable pulley of the secondary pulley, andto regulate an engagement pressure between the belt and each of theprimary pulley and the secondary pulley, an orifice disposed in an oilpassage which is located between the movable pulley of the secondarypulley and the secondary pressure regulating valve, wherein the oilpassage is connected to a feedback hydraulic passage, wherein theorifice is arranged to restrict a flow of the hydraulic fluid betweenthe movable pulley of the secondary pulley and the secondary pressureregulating valve, and a hydraulic pressure sensor disposed between thesecondary pressure regulating valve and the orifice disposed in the oilpassage, and configured to sense the secondary pressure, the controlmethod comprising: sensing the secondary pressure via the hydraulicpressure sensor disposed between the secondary pressure regulating valveand the orifice disposed in the oil passage; setting a target secondarypressure within a strength limit of the belt so as to prevent a slippagebetween the belt and each of the primary pulley and the secondarypulley; switching a shift operation from a normal speed to a high speedhigher than the normal speed when a predetermined condition issatisfied; controlling the secondary pressure regulating valve by afeedback control based on the target secondary pressure and thesecondary pressure sensed by the hydraulic pressure sensor; andmodifying the target secondary pressure by adding a predeterminedquantity when a correction initiation condition is satisfied, thecorrection initiation condition including a first condition that theshift operation is performed at a high speed by switching of theoperation switching section.